Conventionally, there is known a device that monitors a behavior of a person, such as an elderly person, who needs nursing care.
For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2006-175082) discloses a device in which, in order to determine whether a care receiver lying on a bed performs a rising behavior, a watching area is set above the bed, and an image of the watching area is captured with a camera from a lateral direction of the bed. The device estimates that the care receiver performs the rising behavior when a ratio of an image area of the care receiver to the watching area of the image captured with the camera is a predetermined value or more.